Combustion chamber with air inlet means providing a plurality of concentric strata of varying velocities



Nov. 4, 1952 F c. MOCK 2,616,257

COMBUSTION CHAMBER WITH Ali? INLET MEANS PROVIDING A PLURALITY OFCONCENTRIC STRATA OF VARYING VELOCITIES Filed Jan. 9, 1946 2 SHEETSSHEETl zIlI////IIII1". I v 9/ INVENTOR. QAwun'lI/////IIIlIl""' ATTOP/Vf) Nov.4, 1952 F. c. MOCK 2,616,257

COMBUSTION CHAMBER WITH AIR INLET MEANS PROVIDING A PLURALITY OFCONCENTRIC STRATA 0F VARYING VELOCITIES Filed Jan. 9, 1946 2 SHEETSSHEET2 1 N VEN TOR.

FPAA/A d/yam BY W Patented Nov. 4, 1952 COMBUSTION CHAMBER WITH AIRINLET MEANS PROVIDING A PLURALITY F CON QENTR-IC STRATA OF VARYINGVELGCL' TIES Frank C, llrloclr, South Bend, Ind assignor toBendix'A'viation Corporation, South Bend, Ind., a corporation ofDelaware Application January 9, 1946, Serial No. 640,018

The present invention relates to burners, and particularly to burnerswherein a fuel, either gaseous, liquid or powdered solid fuel, isinjected into and burned in a moving column of air. Such burners areparticularly adapted for use in aircraft power plants or engines of thegas turbine and/or jet propulsion types wherein compressed air issupplied to a chamber constituting part of the burner, at which'point itis heated by the combustion of fuel and the expanded air and products ofcombustion discharge through a gas, turbine for driving an aircompressor and/or a propeller, after which the gases may be dis chargedthrough a reaction tube to propel the aircraft or to assist thepropeller in propelling the aircraft. v

This application contains subject matter divided out or my co-pendingapplication Ser. No. 557,812 filed October 9, 1944, now Patent No.2,581,275 plus modifications thereof, and hence may be considered as acontinuation-impart of Ser. No. 557,812.

A burner of the aforesaid type is ofttimes subjected to conditions whichrender it extremelydiificult to maintain stable operation of the burner,or to obtain proper flame propagation and an effective fuel/air ratioover. the wide range of air flows to which the burner is sub jected.Thus, flow of fuel to the burner may at timesbe suddenly reduced toreduce engine speed, resulting in a low flame at the burner nozzle whileat the same time the momentum of the engine may momentarily produce ahigh air flow tending to blow out the flame. Again, it. is de-- sirablethat the burner ignite or start quickly and easily under all conditionsof ai-r flow, both at the start of a flight and during flight of anaircraft. If there is delay in igniting the burner during the initialstarting operation, excess fuel accumulates in both the burner tubeandadjacent chambers, and then when the engine does. start, there is anintense flame and heat produced while the" accumulated fuel is burning.which tends to burn and warp parts in the immediate region of the flame;Another factor is so-called detonation or "blow-gut which may he a causedf'bu'rner failure, particularly at high engine powers, One source or"this noun-e; especially in tubular burners, is" the tendency or theburner to becomeunstame and reverberate somewhat like an organ'pip'e ofsimilar dimensions'; and sometimes these reverberati'onsl build burnerherein disclosed, a separate resonator 7' claims, (or. 39.65)

2 chamber is provided burner tube in communication with the main burnerchamber and having a resonance fre-' quency tending to neutralize ordampen out the reverberations of the main burner chamber or tube.

An object of the invention is to provide a burner or generator of thetype specified which will admit air under pressure into the burnerchamber, and particularly the breech portion thereof in a manner such asto render the burner flame stable under widely varying conditions ofairflow to the burner.

Another and more specific object is to provide a burner or generator forheating and expanding a'ir flowing thereto under pressure havingcalibrated air-inlet means which directs the air into the breech portionof the burner chamber in a plurality of concentric masses or strata ofvarying, velocities with the mass of lowest velocity in the immediateregion of the burner nozzle.

Another object is to provide means in a burner whereby carbon formationon the fuel-delivery nozzle or nozzles as well as on the spark plugs oranalogous ignition means is reduced to a minimum;

Another object is to provide an improved burner or generator unitparticularly adapted for power plants of the gas turbine an/or j'etpropulsion types, and wherein burner failure due to the foregoing andother causes is reduced to a minimum.

A further object is to improve and render more efficient burners or heatgenerators.

The foregoing and other objects and advantages will become apparent inView of the following description taken in conjunction withv thedrawings", wherein:

Figure 1' is a substantially central longitudinal" sectional view of aburner embodying the features of the invention;

Figure 2 is a similar view of a modification structure;

Figure 3 is an end view of Figure 2 taken" as spray nozzle adapted foruse with the burners" illustrated inthe preceding. figures;

Figure 7 is'an' enlarged section of the'end por'- tion of the nozzle ofFigure 6; and" at the breech end of the a rotary compressor, not shown,driven by a I turbine, also not shown, having blades subjected to thedynamic action of heated and expanded air and products of combustiongenerated in the burner.

The burner of Figure l is similar to that disclosed in my copendingapplication above noted; it consists of an outer cylindrical shell orwall 8 provided with a plurality of air inlet ports 9, to which air issupplied under pressure through the chamber 5. Within the breech portionof the outer shell 8 is another shorter cylinder or annulus it} havingan outwardly tapered or inclined bafiie wall I i provided with a seriesof calibrated air inlet orifices !2. Within the annulus I is a third,still shorter cylinder or annulus [3 provided with an end bafile wall l4also formed with a series of air inlet orifices H3. The air impact orbreech end of the burner is provided with a baffle wall l6 formed with aseries of annularlyarranged air-inlet orifices H, is and [9, which arepreferably of progressively decreasing area or flow capacity as theyapproach the center of the said wall l6, said orifices ll, I8 and I9opening into velocity-reducing chambers 20, 2| and 22 defined by thestepped cylinders Ill and I3 and a central bafile wall 23 formed withcalibrated air inlet orifices 24. An ignitor 25, which may be of theelectric sparking type supplied with current from a suitable source, notshown, is projected into the burner cylinder adjacent the tip of aburner nozzle 25. v

To more effectively obtain this velocity-reducing action, the aggregatearea of orifices I2 is greater than the aggregate area of orifices H,the aggregate area of orifices I is greater than the aggregate area oforifices l8, and the aggre-.

gate area of orifices 24 is greater than the aggregatearea of orificesl9.

A combustion chamber constructed in this manner coacts with the fuelfeeding system which supplies fuel to the chamber through the burnernozzle to insure localized fuel/air proportioning and flame propagationthroughout periods of low fuel feeds and permits low fuel feeds at lowair fiows or low power conditions, and also at high air flows as onengine deceleration, without burner failure. Purely. by way of example,it may be desired to meter to the burner nozzle 1.2 pounds of fuel perhour at minimum air fiows or low power conditions and up .to 26.3 poundsof fuel per hour at maximum air flows or full power conditions. A sprayof 1.2 pounds per hour will produce a rather sensitive flame which canbe quickly snuffed out by the sudden injection of air above a certainvelocity, or by an oversupply of air within the region of the flame. Bysuitably calibrating the air inlet and bafile orifices, the velocity ofthe air flowing into the combustion chamber may be adjusted with respectto a pl'urality of combustion zones to insure proper or eflicient flamepropagation at all air flows or power conditions. Thus the velocitywithin the central burner zone in the immediate region of the nozzle 26may be held within a relatively low wall at by means of a wall 5|.

range, for example, of from 9 to 30 feet per second, the velocity withinthe intermediate zone from 18 to 60 feet per second, and within theouter zone from 2'! to feet per second. The total inlet capacity of allthe openings which determine the respective zones should be such as togive the proper amount of air at full power conditions for efficientcombustion with, for example, 6 pounds of fuel per hour. The air flowingthrough the ports 9 may be moving at a velocity of say 36 to feet ormore per second. In order to more effectively diffuse the air as itpasses into the burner chamber, suitable bafiie material such as steelwool or the like, indicated at 21, may be disposed in the chambers 2iand 22, and also in the outer chamber 26 if desired.

Figures 2 and 3 illustrate a burner of modified construction withrespect to Figure l, the burner being illustrated as one of any numberof similar burners mounted within the chamber 5 defined by the annularconcentric walls 6 and "I in the same manner as in Figure 1. The burnerof Figures 2 and 3 comprises an outer shell 40 formed with a series ofhigh velocity air inlet holes 4|, 42 and 42' outwardly from the breechportion thereof. Within the outer shell 40 is mounted a breech assemblycomprising an outer, generally cylindrical member 43 formed withcircumferential rings or bosses 44 and 45' by means of which it may besuitably secured to the shell 40 as by welding or in any other suitablemanner. An annular inwardly or convergingly curved wall 45 forms anextension of the member 43, and another substantially straightcylindrical wall 46 extends forwardly-from the wall 45 and is connectedthereto by web portions or openwor structure defining openings 41.

The cylindrical wall 45 soon becomes heated to a high temperature afterthe burner starts, since it lies in the low flame area, and thereafterit furnishes a hot vaporizing surface against which spray from thenozzle 69 impinges. Among other advantages, this reduces the tendencytoward collection of unburnt fuel in the breech area at low fueldelivery pressures and subsequent explosion and dangerously high heatconditions when the fuel delivery is increased. The openings '47facilitate access of hot gases to the exterior surface of the wall 46.

- An inner breech unit, generally indicated at 48, is provided andcomprises an end wall 48 from the periphery of which a converging orradially-inwardly curved wall 49 projects and is joinedat its inner edgeto a straight cylindrical The walls 49, 50, 5| and adjacent part of thewall 48' form the boundary of a chamber 52; and the end wall 48' isformed with a plurality of calibrated air-inlet openings 53 foradmitting controlled quantities of air to thechamber 52, and from thischamber air maypass into the nozzle area of the breech chamber at areduced velocity through ca1i-' brated holes 54 and 55, the aggregatearea of holes 54 and 55 being greater than the aggregate area of theholes 53.

Between the outer cylindrical member 43: and.

velocity of the air'passing' into the breech chamber immediatelyforwardly of the burner nozzle.

The end wall 48' supports a spray nozzle 60 and a spark plug or othersuitable ignition device 6I.

Airunder pressure moving in a direction from left to right as viewed inFigure 2 is directed into the outer chamber 5 and passes beyond thebreech portion of the burner to the holes 4|, 42,

42' and is fed into the burner chamber at this point at a relativelyhigh velocity of say 215 feet per second; and at the same time air isfed into the annular slots 51, 58 and passes into the breech portion ofthe burner through the expanding chambers 51 and 58' which tend toreduce the velocity of and diffuse the air as it enters the breechchamber. Thus the velocity of the air entering through the outer passage51 might be forty feet per second, while the air entering through theinner pasage might have a velocity of fifteen feet per second. The inletslots 51, 58 and the chambers 51, 58' may be calibrated to provide therequired amount of air at predeterminedvelocities to obtain the mostefficient combustion and flame propagation within the breech area of theburner chamber without danger of blowing out the fiame at theburnernozzle during low fuelfeeds and high air flows.

'The holes 53 admit air into the chamber 52 from which it passes at areduced velocity through the calibrated holes 54 and 55 and is projectedonto the tip of nozzle 60 and also on the exposed outer surface of thespark plug 6|. This controlled supply of air tends to reduce carbonformation by furnishing sufficient oxygen to this region for admixturewith the fine mist of oil, usually present in this area, to supportcombustion, or burn the oil without permitting it to cake on thesurfaces of the nozzle and the plug.

Any convenient method of manufacture of the burner parts may be adopted.For example, the outer shell 40 may be of heat resistant sheet metal,refractory material or the like, while the outer and inner units 43 and48 may be in the form of castings and the intermediate unit 56 of sheetmetal, the parts being joined or bridged by connecting bosses and weldedor otherwise secured together to form a complete assembly. Obviouslyother materials or methods of fabrication may be used.

Figures 4 and 5 illustrate a further modification in burner structurefor carrying out the objects of the present invention. The burner asshown in Figures 4 and 5. is mounted in a chamber'5 similar to theburners of Figures 1 and 2; it comprises an outer shell 10 formed with aseries of holes 1|, 1| outwardly from the breech portion of the burner,for admitting high-velocity air into the burner along the lengththereof. The breech portion of the burner comprises a unit having anendwall 12, which as shown is of radially outwardly stepped construction,and projecting forwardly from theend wall are a series of concentriccylindrical walls 13, 14 and 15 which define a plurality of chambers 16and 11, a main breech chamber '18 and a supplemental breech chamber 18'.A wall 13' surrounds the breech chamber forwardly of the nozzle, toprovide .a vaporizing surface in a manner similar to the wall 46 of Fig.2. The outer face walls of the chambers 16 and 11 are supplied with airthrough a plurality of openings 19 and 19', preferably arrangedtangentially in order to produce a baffle effect by causing the airtopass into the chambers 1'6 and 11 to be broken up or have its velocityreduced-by circulation and frictionless This obviates the need for ber82 which is supplied with. air through ann-ular slots 83. and holes83'.' V

The end wall 12 may be bored or cast with holes or. suitable openings toreceive a spray nozzle 84 and a spark plug 85.

Air at highvelocity entering the chamber 5 from left toright as viewedin Figure 4 is directed into. the holes 1| and 1| at for example 215feet per second. Air also impacts the end breech wall '12 and is fedthrough the tangential holes 19 and 19 into the chambers 16 and 11 whichaction reduces the velocity of the air in the manner heretoforeexplained, and from these -cham-- bers the air is fed into the breechchamber 18- at a somewhat further reduced velocity through the annularseries of holes 83 and 8!. example, the air entering the breech chamberthrough the holes 89 may be at a velocity of forty' feet per second;while the air entering the breech chamber through the holes BI may be ata velocity of fifteen feet per second. The whirling motion imparted tothe air entering chambers 16 and 11 also tends to distribute the airequally through out the area of the said chambers before passing intothe breech chamber 18. If desired, additional holes may be formed in thewall 15 to direct air against the tip of the nozzle 84 and the sparkplug and furnish sufiicient oxygen to support combustion in theimmediate region of the nozzle tip and the spark plug and thereby reducethe tendency toward carbon formation on thes parts.

While any suitable type of fuel spray nozzle '25, 60 or 84 may be used,it is preferred to use a nozzle which will operate to discharge aconeshaped spray of fuel when the latter is under low pressures in thearea of lowest velocity of the incoming air, and as the fuel deliverypressure increases, the fuel spray cone will progressively lengthen andintersect the respective masses or strata of incoming air. A nozzlesuitable foruse with burners of the type herein disclosed is shown inFigures 6, '1 and 8.

The nozzle illustrated in Figures 6, 7 and 8 consists of a flanged body90 having therein av spray head 9| provided with a stem 92 encircled bya spring 93 which urges the head to seated position with th fiared tipor end portion thereof engaging in the similarly-contoured maindischarge orifice or jet 94. A cap 95 is threaded on the rear extremityof the body 99, and between this cap and the body flange is a fitting 96having a tubular portion 91 to which a fuel supply tube 98 is connected.Fuel passes into nozzle chamber 99 through ports I00; and at lowpressures flows through small bores I 0 I formedin the spray head, noteFigure '7, at a tangent to a central cavity or recess I02 having thereina member I03 provided with a small lowpressure discharge orifice I94.The seating tension of spring 93 is adjustable by means of thrust nutI95 and lock nut I96. The tangential arrangement of the bores I0l,causes the spray to swirl as it leaves the low pressure orifice at anangle determined by the relative areas of bores or passages NH and I04.

The tension of spring 93 may be adjusted to Between the outerv Thus,fora point where at predetermined low pressure the spray head 9| remainsseated and discharge is by way of small bores NH and low pressuredischarge orifice I04, but as pressure builds up, discharge isprincipally through the high pressure discharge orifice 94 with acertain additional discharge through orifice I04, the spray issuing athigh pressures in a cone-shaped fog, the spray cone angle beingdetermined by the angle of the cone-shaped head 9!. Thus at low fuelpressures when the air is likewise at its lowest pressure, the velocityof the fuel is steppedup by the small bores l0! and small jet I04, whileat higher pressures, the outer cone-shaped discharge orifice takes over,producing a welldifiused spray in all directions. The adjustability ofthe spray head permits accurate synchronization of an entire set ofburner nozzles.

As heretofore noted, burners of the type with which the presentinvention is primarily concerned are subject to a building up ofreverberations, particularly at high air flows and rich fuel air ratios,which may reach an intensity such as to cause the burner flame to becomeextremely unstable and finally fail entirely; it is characterized by anirregular exhaust sound accompanied by an irregular flame length and astrong odor of unburnt fuel. In the burner disclosed herein, any orallof the breech chambers 20, 2| and 22 of Figure 1, 52 of Figure 2, or16 and 11 of Figure 4, may have an individual resonance frequency whichis variable in direct relation to the volume of the resonance chamberand the area of its air-inlet and discharge ports,

and since these chambers have a resonance fre-- quency different fromthat of the main burner chamber or tube at a given air flow and fuelfeed, their resonance frequencies tend to neutralize or dampen out thereverberations of the main burner chamber. Such resonance chamber, whilepreferably having air-inlet and discharge ports, need only have thelatter ports, or need only be in communication with the breech or mainburner chamber to function as a reverberation dampener.

It will be understood that the drawings are simply illustrative, andthat certain changes in construction, design and arrangement of threspective parts fall within the scope of the invention as defined bythe appended claims.

I claim:

1. In a generator for heating and expanding air flowing thereto underpressure, an outer shell defining an elongated combustion chamberprovided with a fuel-discharge nozzle at one nd thereof, an end wallmounting said nozzl and having a series of calibrated air-inlet orificesof varying flow capacity arranged in generally annular formation withthe orifices of lowest flow capacity located centrally of said wall andthe remaining orifices progressively increasing in capacity as theyapproach the periphery of the wall, a plurality of spaced annuliprojecting forwardly from said end Wall to provide flow passages for theair admitted through said orifices and at their inner ends terminatingin spaced stepped relation with the shortest annulus surrounding saidnozzle, and bafiles coacting with said annuli and adapted to reduce thevelocity of the air flowing into the combustion chamber in the region ofthe nozzle through said calibrated air-inlet orifices.

In a generator for heating and expanding air flowing thereto underpressure, an outer shell defining an elongated generally cylindricalcombustion chamber provided with an end wall mounting a fuel-dischargenozzle, said end wall being provided with a series of calibratedairinlet orifices of varying area or flow capacity with the orifices oflowest flow capacity surrounding the nozzle and the remaining orificesprogressively increasing in area as they approach the periphery of thewall, a plurality of substantially cylindrical walls projecting fromsaid end wall and arranged in spaced substantially concentric formationand at their inner ends terminating in stepped relation with theshortest annulus surrounding the nozzle, said annuli separating theinlet or breech end of the combustion chamber into a plurality ofsub-chambers which tend to equalize the air flowin in through saidair-inlet orifices, and baflie means coactlng with said latter chambersconstructed and arranged to direct the air into the combustion chamberin masses of reduced and varying velocities with the mass of lowestvelocity in the immediate leg of the nozzle.

3. In a generator or burner for heating and expanding air flowingthereto under pressure, an outer shell defining a combustion chamberhaving a breech portion at one extremity thereof, a breech unit at theair-inlet end of said breech portion provided with an end wall formedwith a plurality of radially spaced air-inlet openings, a series ofradially-inwardly converging substantially cylindrical radially-spacedwalls projecting forwardly from said openings and defining a pluralityof air passages of gradually increasing cross-sectional area adapted todirect air into the breech portion of the combustion chamber, saidpassages receiving air from said inlet openings and producing anexpansion efiect on the air as it flows therethrough to 'reduce thevelocity thereof and diffuse the air as it passes into the said breechportion.

4. In a generator or burner for heating and expanding air flowingthereto under pressure, an outer substantially cylindrical shelldefining a combustion chamber having an air inlet or breech portion atone extremity thereof, a breech unit at the air inlet end of saidchamber made up of a series of outer substantially concentric cylindersand a central member having an end wall mounting a fuel spray nozzle,said outer I cylinders having their rear edges lying in the plane ofsaid end wall and arranged in radiallyspaced relation to provideair-inlet openings, the walls of said cylinders projecting forwardlyfrom said openings in axially converging formation and inprogressively-increasing radially-spaced relation to define air inletpassages tending to expand the air entering the breech portion of thecombustion chamber and reduce the velocity 5. In a generator or burnerfor heating and expanding air flowing thereto under pressure, an outersubstantially cylindrical shell defining a main combustion chamberhaving a breech portion at the air-inlet extremity thereof, a breechunit for controlling the supply of air to said chamber including anouter substantially cylindrical wall projecting forwardly inradiallyinwardly-curved formation into said breech portion, anothersubstantially similarly shaped cylindrical wall arranged concentricallywithin said first-named cylindrical wall, said walls projectingforwardly in progressively radially-spaced relation to define a seriesof air-inlet passages of gradually increasing cross-sectional area whichtend to expand the air and reduce the velocity thereof as it flows intothe breech portion of the combustion chamber.

6. In a generator or burner for heating and expanding air flowingthereto under pressure, an outer shell defining a main combustionchamber having a breech portion at one extremity thereof, an end walloverlying the air-inlet end of said breech portion, a fuel spray nozzlelocated in said breech portion, a plurality of radially-spaced wallsprojecting forwardly from said end wall into said breech portion anddefining a plurality of air chambers therebetween in restrictedcommunication with said breech portion, a series oftangentially-disposed air-inlet passages for admitting air to said airchambers in a manner such as to produce a baflle effect on the air andat the same time facilitate distribution of the air in said latterchambers.

7. In a generator or burner for heating and expanding air flowingthereto under pressure, an outer substantially cylindrical shelldefining a main combustion chamber having a breech portion at oneextremity thereof, a breech unit mounted in the air inlet end of saidshell and comprising an end wall lying in a plane generally normal tothe axis of said combustion 10 chamber and a plurality of substantiallycylindrical radially-spaced walls projecting forwardly from said endwall into said breech portion, said cylindrical walls defining aplurality of air chambers surrounding said breech portion and inrestricted flow communication therewith, said end wall being providedwith a series of tangentiallydisposed air-inlet holes for communicatingair to said air chambers and at the same time produce a baiile effect onthe air and facilitate distribution thereof in said latter chambers,said shell being formed with a series of air inlet openings forwardly ofsaid breech portion.

FRANK C. MOCK.

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